A novel in vitro system was developed to investigate the effects of two forms of calcined mesopor... more A novel in vitro system was developed to investigate the effects of two forms of calcined mesoporous silica particles (MCM41-cal and SBA15-cal) on cellular respiration of mouse tissues. O2 consumption by lung, liver, kidney, spleen, and pancreatic tissues was ...
Cardiovascular complications are common in type 1 diabetes mellitus (TIDM) and there is an increa... more Cardiovascular complications are common in type 1 diabetes mellitus (TIDM) and there is an increased risk of arrhythmias as a result of dysfunction of the cardiac conduction system (CCS). We have previously shown that, in vivo, there is a decrease in the heart rate and prolongation of the QRS complex in streptozotocin-induced type 1 diabetic rats indicating dysfunction of the CCS. The aim of this study was to investigate the function of the ex vivo CCS and key proteins that are involved in pacemaker mechanisms in TIDM. RR interval, PR interval and QRS complex duration were significantly increased in diabetic rats. The beating rate of the isolated sinoatrial node (SAN) preparation was significantly decreased in diabetic rats. The funny current density and cell capacitance were significantly decreased in diabetic nodal cells. Western blot showed that proteins involved in the function of the CCS were significantly decreased in diabetic rats, namely: HCN4, Ca v 1.3, Ca v 3.1, Cx45, and NCX1 in the SAN; RyR2 and NCX1 in the atrioventricular junction and Cx40, Cx43, Cx45, and RyR2 in the Purkinje network. We conclude that there are complex functional and cellular changes in the CCS in TIDM. The changes in the proteins involved in the function of this electrical system are expected to adversely affect action potential generation and propagation, and these changes are likely to be arrhythmogenic.
We have investigated the effects of acute acidosis on ventricular myocyte shortening and intracel... more We have investigated the effects of acute acidosis on ventricular myocyte shortening and intracellular Ca 2+ in streptozotocin (STZ)-induced diabetic rat. Shortening and intracellular Ca 2+ were measured in electrically stimulated myocytes superfused with either normal Tyrode solution pH adjusted to either 7.4 (control solution) or 6.4 (acid solution). Experiments were performed at 35-36 • C. At 8-12 weeks after treatment, the rats that received STZ had lower body and heart weights compared to controls, and blood glucose was characteristically increased. Contractile defects in myocytes from diabetic rat were characterized by prolonged time to peak shortening. Superfusion of myocytes from control and diabetic rats with acid solution caused a significant reduction in the amplitude of shortening; however, the magnitude of the response was not altered by STZ treatment. Acid solution also caused significant and quantitatively similar reductions in the amplitude of Ca 2+ transients in myocytes from control and diabetic rats. Effects of acute acidosis on amplitude of myocyte contraction and Ca 2+ transient were not significantly altered by STZ treatment. Altered myofilament sensitivity to Ca 2+ and altered mechanisms of sarcoplasmic reticulum Ca 2+ transport might partly underlie the acidosis-evoked reduction in amplitude of shortening in myocytes from control and STZ-induced diabetic rat. (Mol Cell Biochem xxx: 1-7, 2004)
Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a d... more Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca 2+ , measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88 ± 2 ms and 107 ± 4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca 2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.
Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. ... more Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. Here, we investigate the reason for increased microtubule stability, and the functional consequences of stable microtubule disruption. Ventricular myocytes were isolated from rats at 8-12 weeks after injection of STZ. A 10% increase in microtubule density, but no difference in the ratio of microtubule-associated protein 4 (MAP4) to tubulin was seen in myocytes from STZ rats. Functionally, STZ myocytes showed a tendency for reduced shortening and intracellular Ca2+ ([Ca2+]i) transient amplitude, and a significant prolongation of time to peak (ttp) shortening and [Ca2+]i. Although microtubules in STZ myocytes were less sensitive to the microtubule disruptor nocodazole (NOC; 33 microM) than control myocytes, we only saw marked functional consequences of microtubule disruption by NOC in myocytes from diabetic animals. NOC increased shortening and [Ca2+]i transient amplitude in STZ myocytes by 45 and 24%, respectively (compared with 4 and 6% in controls). Likewise, NOC decreased ttp shortening and [Ca2+]i only in STZ myocytes, such that these parameters were no longer different between the two groups. In conclusion, stable microtubules in diabetes are not associated with an increase in MAP4, but are functionally relevant to cardiac dysfunction in diabetes, regulating both [Ca2+]i and shortening.
Alloxan is widely used to induce diabetes mellitus in experimental animals. Recent studies have p... more Alloxan is widely used to induce diabetes mellitus in experimental animals. Recent studies have provided evidence that alloxan has direct actions on cardiac muscle contraction. The aim of this study was to further investigate the mechanisms underlying the effects of alloxan on ventricular myocyte shortening and intracellular Ca(2+) transport. Amplitude of myocyte shortening was reduced in a dose-dependent manner as the concentration of alloxan was increased in the range 10(-7)-10(-4) M. Amplitude of shortening was reduced (56.8 +/- 6.6%, n = 27) by 10(-6) M alloxan and was partially reversed during a 10 min washout. Amplitude of the Ca(2+) transient was also reduced (79.7 +/- 2.9%, n = 29) by 10(-6) M alloxan. Caffeine-evoked sarcoplasmic reticulum Ca(2+) release, fractional release of Ca(2+), assessed by comparing the amplitude of electrically evoked with that of caffeine-evoked Ca(2+) transients, and fura-2-cell length trajectory during the late stages of relaxation of myocyte twitch contraction were not significantly altered by alloxan. The amplitude of L-type Ca(2+) current was not altered by alloxan. Alterations in sarcoplasmic reticulum Ca(2+) transport, myofilament sensitivity to Ca(2+), and L-type Ca(2+) current do not appear to underlie the negative inotropic effects of alloxan.
Contraction and intracellular free Ca2+ concentrations (Ca2+)i in ventricular myocytes from rats ... more Contraction and intracellular free Ca2+ concentrations (Ca2+)i in ventricular myocytes from rats receiving sucrose-enriched diets (SED's) were investigated. Groups of Wistar rats received normal rat chow together with either normal drinking water or water containing 500 mM sucrose ad libitum . Experiments were performed 12-14 weeks later. Rats receiving SED's responded differently to a standard glucose tolerance test. Fasting blood glucose levels in SED and control rats were 59.4±1.3 and 58.8±1.4 mg/dl, respectively. At 30 min after intraperitoneal administration of glucose (2g/kg body weight) concentrations of blood glucose were significantly (P0.05) different when compared to initial fasting blood glucose values. Blood plasma insulin concentrations in SED and control rats were 3.01±0.55 (5) and 0.29±0.05 (5) ng/ml, respectively. Amplitude and time to peak (TPK) of ventricular myocyte shortening and Ca2+ transient were not altered by SED. Time to half (THALF) relaxation of ...
Contraction and intracellular Ca2+ in ventricular myocytes from rats receiving fructose-enriched ... more Contraction and intracellular Ca2+ in ventricular myocytes from rats receiving fructose-enriched diets (FED) were investigated. Groups of male Wistar rats received normal rat chow together with either normal drinking water or water containing 500 mM fructose ad libitum. Experiments were performed 12-14 weeks later. Rats receiving FED responded differently to a standard glucose tolerance test. Fasting blood glucose levels in
Background: Exposure to pesticides and industrial toxins are implicated in cardiovascular disease... more Background: Exposure to pesticides and industrial toxins are implicated in cardiovascular disease. Paraquat (PAR) is a toxic chemical widely used as an herbicide in developing countries and described as a major suicide agent. The hypothesis tested here is that PAR induced myocardial dysfunction may be attributed to altered mechanisms of Ca 2+ transport which are in turn possibly linked to oxidative stress. The mechanisms of PAR induced myocardial dysfunction and the impact of antioxidant protection was investigated in rat ventricular myocytes. Methodology: Forty adult male Wistar rats were divided into 4 groups receiving the following daily intraperitoneal injections for 3 weeks: Group 1 PAR (10 mg/kg), Control Group 2 saline, Group 3 vitamin E (100 mg/kg) and Group 4 PAR (10 mg/kg) and vitamin E (100 mg/kg). Ventricular action potentials were measured in isolated perfused heart, shortening and intracellular Ca 2+ in electrically stimulated ventricular myocytes by video edge detection and fluorescence photometry techniques, and superoxide dismutase (SOD) and catalase (CAT) levels in heart tissue.
Streptozotocin (STZ) and alloxan (ALX) are widely used to induce diabetes mellitus in experimenta... more Streptozotocin (STZ) and alloxan (ALX) are widely used to induce diabetes mellitus in experimental animals. The direct effects of STZ and ALX on the amplitude and time course of ventricular myocyte shortening and on cardiac action potentials were investigated. STZ and ALX (10 −5 M) were dissolved in normal Tyrode (NT), maintained at pH 7.4 and 37 • C and stored for either 15 or 60-120 min. Both compounds reduced the amplitude of myocyte shortening. Compared to NT the amplitude of shortening was 34.7 ± 5.0% and 35.2 ± 6.8% with STZ and 41.0 ± 5.5% and 37.3 ± 5.7% with ALX stored for 15 and 60-120 min, respectively. During a 10 min NT washout STZ myocytes recovered to 56.2 ± 8.3% and 60.5 ± 8.2% and ALX myocytes recovered to 88.9 ± 10.0% and 83.7 ± 9.9% after storage of compounds for 15 and 60-120 min, respectively. Perfusion of the whole heart with ALX induced bradycardia but had no effects on the duration of action potential repolarization at 50% and 70% from peak action potential. The negative inotropic effects of STZ and ALX were not altered by storage. The results suggest that some of the effects on heart reported in STZ-and ALX-induced diabetes may be partly attributed to direct action of these compounds.
Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. ... more Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. Here, we investigate the reason for increased microtubule stability, and the functional consequences of stable microtubule disruption. Ventricular myocytes were isolated from rats at 8-12 weeks after injection of STZ. A 10% increase in microtubule density, but no difference in the ratio of microtubule-associated protein 4 (MAP4) to tubulin was seen in myocytes from STZ rats. Functionally, STZ myocytes showed a tendency for reduced shortening and intracellular Ca2+ ([Ca2+]i) transient amplitude, and a significant prolongation of time to peak (ttp) shortening and [Ca2+]i. Although microtubules in STZ myocytes were less sensitive to the microtubule disruptor nocodazole (NOC; 33 microM) than control myocytes, we only saw marked functional consequences of microtubule disruption by NOC in myocytes from diabetic animals. NOC increased shortening and [Ca2+]i transient amplitude in STZ myocytes by 45 and 24%, respectively (compared with 4 and 6% in controls). Likewise, NOC decreased ttp shortening and [Ca2+]i only in STZ myocytes, such that these parameters were no longer different between the two groups. In conclusion, stable microtubules in diabetes are not associated with an increase in MAP4, but are functionally relevant to cardiac dysfunction in diabetes, regulating both [Ca2+]i and shortening.
Cardiac dysfunction is a frequently reported complication of clinical and experimental diabetes m... more Cardiac dysfunction is a frequently reported complication of clinical and experimental diabetes mellitus. Streptozotocin (STZ)-induced diabetes in rat is associated with a variety of cardiac defects including disturbances to heart rhythm and prolonged time-course of cardiac muscle contraction and/or relaxation. The effects of carbenoxolone (CBX), a selective gap junction inhibitor, on heart rhythm and contractility in STZ-induced diabetic rat have been investigated. Heart rate was significantly (P < 0.05) reduced in Langendorff perfused spontaneously beating diabetic rat heart (171+/-12 BPM) compared to age-matched controls (229+/- 9 BPM) and further reduced by 10(-5) M CBX in diabetic (20%) and in control (17%) hearts. Action potential durations (APDs), recorded on the epicardial surface of the left ventricle, were prolonged in paced (6 Hz) diabetic compared to control hearts. Perfusion of hearts with CBX caused further prolongation of APDs and to a greater extent in control compared to diabetic heart. Percentage prolongation at 70% from the peak of the action potential amplitude after CBX was 18% in diabetic compared to 48% in control heart. CBX had no significant effect on resting cell length or amplitude of ventricular myocyte shortening in diabetic or control rats. However, resting fura-2 ratio (indicator for intracellular Ca(2+) concentration) and amplitude of the Ca(2+) transient were significantly (P < 0.05) reduced by CBX in diabetic rats but not in controls. In conclusion the larger effects of CBX on APD in control ventricle and the normalizing effects of CBX on intracellular Ca(2+) in ventricular myocytes from diabetic rat suggest that there may be alterations in gap junction electrophysiology in STZ-induced diabetic rat heart.
Ventricular electrical conduction has been investigated in the streptozotocin (STZ)-induced diabe... more Ventricular electrical conduction has been investigated in the streptozotocin (STZ)-induced diabetic rat. Diabetes was induced with a single injection of STZ (60 mg/kg bodyweight, ip). The ECG was measured continuously, in vivo, using a biotelemetry system. Left ventricular action potentials were recorded with an extracellular suction electrode. Expression of mRNA transcripts for selected ion transport proteins was measured in left ventricle with real-time RT-PCR. At 10 weeks after STZ treatment, in vivo heart rate (HR) was reduced (267 +/- 3 vs. 329 +/- 5 BPM), QRS complex duration and QT interval were prolonged in diabetic rats compared to controls. In vitro spontaneous HR was reduced and paced heart action potential repolarization was prolonged in diabetic rats compared to controls. The mRNA expression for Kcnd2 (I (to) channel) and Kcne2 (I (kr) channel) was significantly reduced in diabetic rats compared to controls. Altered gene expression and, in particular, genes that encode K(+) channel proteins may underlie delayed propagation of electrical activity in the ventricular myocardium of STZ-induced diabetic rat.
Diabetes induces changes in the structural, biochemical, electrical, and contractile properties o... more Diabetes induces changes in the structural, biochemical, electrical, and contractile properties of skeletal muscles. Neuropeptide Y (NPY) administered locally can induce angiogenesis in a rat ischemic limb model and restore the contractile function of the ischemic muscle. The effects of NPY on the contractile characteristics of limb skeletal muscles were examined in streptozotocin-induced diabetic rats. Rats were treated with sham pellets (control groups) or NPY-containing pellets (1 mg of NPY/pellet, 14 days releasing time) administered locally to the rat hind limb 2 months after induction of diabetes. Contractile properties and fatigability of the slow-twitch soleus and fast-twitch gastrocnemius medials muscle were compared in control (sham), control NPY, diabetic (sham), and diabetic NPY groups. In order to induce fatigue trains of repetitive tetanic stimulation were used (600 ms/1 s simulation-rest cycle per train, 112 trains at an 85-Hz fusion frequency). Two months of untreated diabetes significantly prolonged soleus contraction and slowed its relaxation, but had minimal effects on soleus tension. NPY ameliorated the diabetic effects on soleus speed-related contractile properties, restoring its contraction and relaxation times. Diabetes significantly reduced gastrocnemius medials tetanic tension, leaving its contractile characteristics mostly unaffected. NPY partially restored gastrocnemius tetanic tension production capacity. Diabetes significantly increased fatigability of both muscles, which was partially restored by NPY, as evidenced by restored endurance of soleus muscle. The results suggest that NPY administered locally tends to normalize muscle performance and improve fatigue resistance of skeletal muscles in streptozotocin diabetes. Further examination is needed to establish the mechanisms of local NPY action on muscle contractile properties in streptozotocin-induced diabetes.
Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a d... more Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca 2+ , measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88 ± 2 ms and 107 ± 4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca 2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.
Diabetes mellitus is a serious global health problem, and cardiovascular complications are the ma... more Diabetes mellitus is a serious global health problem, and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. The chronic effects of neonatal alloxan-(ALX) induced diabetes mellitus on ventricular myocyte contraction and intracellular Ca 2? transport have been investigated. Ventricular myocyte shortening was measured with a video edge detection system and intracellular Ca 2? was measured in fura-2 loaded cells by fluorescence photometry. Diabetes was induced in 5-day old male Wistar rats by a single intraperitoneal injection of ALX (200 mg/kg body weight). Experiments were performed 12 months after ALX treatment. Fasting blood glucose was elevated and blood glucose at 60, 120 and 180 min after a glucose challenge (2 g/kg body weight, intraperitoneal) was elevated in diabetic rats compared to age-matched controls. Amplitude of shortening was significantly (P \ 0.05) reduced in electrically stimulated myocytes from diabetic hearts (5.70 ± 0.24%) compared to controls (6.48 ± 0.28%). Amplitude of electrically evoked Ca 2? transients was also significantly (P \ 0.05) reduced in myocytes from diabetic hearts (0.11 ± 0.01 fura-2 ratio units) compared to controls (0.15 ± 0.01 fura-2 ratio units). Fractional sarcoplasmic reticulum Ca 2? release was not significantly (P [ 0.05) altered in myocytes from diabetic heart (0.70 ± 0.03 fura-2 ratio units) compared to controls (0.72 ± 0.03 fura-2 ratio units). Amplitude of caffeine-stimulated Ca 2? transients was significantly (P \ 0.05) reduced in myocytes from diabetic hearts (0.43 ± 0.02 fura-2 ratio units) compared to controls (0.51 ± 0.03 fura-2 ratio units). Area under the caffeine-evoked Ca 2? transient was significantly (P \ 0.05) reduced in myocytes from diabetic heart (0.77 ± 0.06 Vsec) compared to controls (1.14 ± 0.12 Vsec). Intracellular Ca 2? refilling rate during electrical stimulation following application of caffeine was significantly (P \ 0.05) slower in myocytes from diabetic heart (0.013 ± 0.001 V/sec) compared to controls (0.031 ± 0.007 V/sec). Depressed shortening may be partly attributed to depressed sarcoplasmic reticulum Ca 2? transport in myocytes from neonatal ALX-induced diabetic rat heart. Keywords Neonatal alloxan-induced diabetes mellitus Á Alloxan-induced diabetes mellitus Á Type 2 diabetes mellitus Á Cardiac muscle contraction Á Intracellular Ca 2? transport Á Ventricular myocyte shortening
In this article, the name of the last co-author is given as Ljubisavijevic M. Dr. Ljubisavljevic ... more In this article, the name of the last co-author is given as Ljubisavijevic M. Dr. Ljubisavljevic surname is misspelled. His correct name should read ''Ljubisavljevic M''. Everything else in this article remains correct.
A novel in vitro system was developed to investigate the effects of two forms of calcined mesopor... more A novel in vitro system was developed to investigate the effects of two forms of calcined mesoporous silica particles (MCM41-cal and SBA15-cal) on cellular respiration of mouse tissues. O2 consumption by lung, liver, kidney, spleen, and pancreatic tissues was ...
Cardiovascular complications are common in type 1 diabetes mellitus (TIDM) and there is an increa... more Cardiovascular complications are common in type 1 diabetes mellitus (TIDM) and there is an increased risk of arrhythmias as a result of dysfunction of the cardiac conduction system (CCS). We have previously shown that, in vivo, there is a decrease in the heart rate and prolongation of the QRS complex in streptozotocin-induced type 1 diabetic rats indicating dysfunction of the CCS. The aim of this study was to investigate the function of the ex vivo CCS and key proteins that are involved in pacemaker mechanisms in TIDM. RR interval, PR interval and QRS complex duration were significantly increased in diabetic rats. The beating rate of the isolated sinoatrial node (SAN) preparation was significantly decreased in diabetic rats. The funny current density and cell capacitance were significantly decreased in diabetic nodal cells. Western blot showed that proteins involved in the function of the CCS were significantly decreased in diabetic rats, namely: HCN4, Ca v 1.3, Ca v 3.1, Cx45, and NCX1 in the SAN; RyR2 and NCX1 in the atrioventricular junction and Cx40, Cx43, Cx45, and RyR2 in the Purkinje network. We conclude that there are complex functional and cellular changes in the CCS in TIDM. The changes in the proteins involved in the function of this electrical system are expected to adversely affect action potential generation and propagation, and these changes are likely to be arrhythmogenic.
We have investigated the effects of acute acidosis on ventricular myocyte shortening and intracel... more We have investigated the effects of acute acidosis on ventricular myocyte shortening and intracellular Ca 2+ in streptozotocin (STZ)-induced diabetic rat. Shortening and intracellular Ca 2+ were measured in electrically stimulated myocytes superfused with either normal Tyrode solution pH adjusted to either 7.4 (control solution) or 6.4 (acid solution). Experiments were performed at 35-36 • C. At 8-12 weeks after treatment, the rats that received STZ had lower body and heart weights compared to controls, and blood glucose was characteristically increased. Contractile defects in myocytes from diabetic rat were characterized by prolonged time to peak shortening. Superfusion of myocytes from control and diabetic rats with acid solution caused a significant reduction in the amplitude of shortening; however, the magnitude of the response was not altered by STZ treatment. Acid solution also caused significant and quantitatively similar reductions in the amplitude of Ca 2+ transients in myocytes from control and diabetic rats. Effects of acute acidosis on amplitude of myocyte contraction and Ca 2+ transient were not significantly altered by STZ treatment. Altered myofilament sensitivity to Ca 2+ and altered mechanisms of sarcoplasmic reticulum Ca 2+ transport might partly underlie the acidosis-evoked reduction in amplitude of shortening in myocytes from control and STZ-induced diabetic rat. (Mol Cell Biochem xxx: 1-7, 2004)
Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a d... more Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca 2+ , measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88 ± 2 ms and 107 ± 4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca 2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.
Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. ... more Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. Here, we investigate the reason for increased microtubule stability, and the functional consequences of stable microtubule disruption. Ventricular myocytes were isolated from rats at 8-12 weeks after injection of STZ. A 10% increase in microtubule density, but no difference in the ratio of microtubule-associated protein 4 (MAP4) to tubulin was seen in myocytes from STZ rats. Functionally, STZ myocytes showed a tendency for reduced shortening and intracellular Ca2+ ([Ca2+]i) transient amplitude, and a significant prolongation of time to peak (ttp) shortening and [Ca2+]i. Although microtubules in STZ myocytes were less sensitive to the microtubule disruptor nocodazole (NOC; 33 microM) than control myocytes, we only saw marked functional consequences of microtubule disruption by NOC in myocytes from diabetic animals. NOC increased shortening and [Ca2+]i transient amplitude in STZ myocytes by 45 and 24%, respectively (compared with 4 and 6% in controls). Likewise, NOC decreased ttp shortening and [Ca2+]i only in STZ myocytes, such that these parameters were no longer different between the two groups. In conclusion, stable microtubules in diabetes are not associated with an increase in MAP4, but are functionally relevant to cardiac dysfunction in diabetes, regulating both [Ca2+]i and shortening.
Alloxan is widely used to induce diabetes mellitus in experimental animals. Recent studies have p... more Alloxan is widely used to induce diabetes mellitus in experimental animals. Recent studies have provided evidence that alloxan has direct actions on cardiac muscle contraction. The aim of this study was to further investigate the mechanisms underlying the effects of alloxan on ventricular myocyte shortening and intracellular Ca(2+) transport. Amplitude of myocyte shortening was reduced in a dose-dependent manner as the concentration of alloxan was increased in the range 10(-7)-10(-4) M. Amplitude of shortening was reduced (56.8 +/- 6.6%, n = 27) by 10(-6) M alloxan and was partially reversed during a 10 min washout. Amplitude of the Ca(2+) transient was also reduced (79.7 +/- 2.9%, n = 29) by 10(-6) M alloxan. Caffeine-evoked sarcoplasmic reticulum Ca(2+) release, fractional release of Ca(2+), assessed by comparing the amplitude of electrically evoked with that of caffeine-evoked Ca(2+) transients, and fura-2-cell length trajectory during the late stages of relaxation of myocyte twitch contraction were not significantly altered by alloxan. The amplitude of L-type Ca(2+) current was not altered by alloxan. Alterations in sarcoplasmic reticulum Ca(2+) transport, myofilament sensitivity to Ca(2+), and L-type Ca(2+) current do not appear to underlie the negative inotropic effects of alloxan.
Contraction and intracellular free Ca2+ concentrations (Ca2+)i in ventricular myocytes from rats ... more Contraction and intracellular free Ca2+ concentrations (Ca2+)i in ventricular myocytes from rats receiving sucrose-enriched diets (SED's) were investigated. Groups of Wistar rats received normal rat chow together with either normal drinking water or water containing 500 mM sucrose ad libitum . Experiments were performed 12-14 weeks later. Rats receiving SED's responded differently to a standard glucose tolerance test. Fasting blood glucose levels in SED and control rats were 59.4±1.3 and 58.8±1.4 mg/dl, respectively. At 30 min after intraperitoneal administration of glucose (2g/kg body weight) concentrations of blood glucose were significantly (P0.05) different when compared to initial fasting blood glucose values. Blood plasma insulin concentrations in SED and control rats were 3.01±0.55 (5) and 0.29±0.05 (5) ng/ml, respectively. Amplitude and time to peak (TPK) of ventricular myocyte shortening and Ca2+ transient were not altered by SED. Time to half (THALF) relaxation of ...
Contraction and intracellular Ca2+ in ventricular myocytes from rats receiving fructose-enriched ... more Contraction and intracellular Ca2+ in ventricular myocytes from rats receiving fructose-enriched diets (FED) were investigated. Groups of male Wistar rats received normal rat chow together with either normal drinking water or water containing 500 mM fructose ad libitum. Experiments were performed 12-14 weeks later. Rats receiving FED responded differently to a standard glucose tolerance test. Fasting blood glucose levels in
Background: Exposure to pesticides and industrial toxins are implicated in cardiovascular disease... more Background: Exposure to pesticides and industrial toxins are implicated in cardiovascular disease. Paraquat (PAR) is a toxic chemical widely used as an herbicide in developing countries and described as a major suicide agent. The hypothesis tested here is that PAR induced myocardial dysfunction may be attributed to altered mechanisms of Ca 2+ transport which are in turn possibly linked to oxidative stress. The mechanisms of PAR induced myocardial dysfunction and the impact of antioxidant protection was investigated in rat ventricular myocytes. Methodology: Forty adult male Wistar rats were divided into 4 groups receiving the following daily intraperitoneal injections for 3 weeks: Group 1 PAR (10 mg/kg), Control Group 2 saline, Group 3 vitamin E (100 mg/kg) and Group 4 PAR (10 mg/kg) and vitamin E (100 mg/kg). Ventricular action potentials were measured in isolated perfused heart, shortening and intracellular Ca 2+ in electrically stimulated ventricular myocytes by video edge detection and fluorescence photometry techniques, and superoxide dismutase (SOD) and catalase (CAT) levels in heart tissue.
Streptozotocin (STZ) and alloxan (ALX) are widely used to induce diabetes mellitus in experimenta... more Streptozotocin (STZ) and alloxan (ALX) are widely used to induce diabetes mellitus in experimental animals. The direct effects of STZ and ALX on the amplitude and time course of ventricular myocyte shortening and on cardiac action potentials were investigated. STZ and ALX (10 −5 M) were dissolved in normal Tyrode (NT), maintained at pH 7.4 and 37 • C and stored for either 15 or 60-120 min. Both compounds reduced the amplitude of myocyte shortening. Compared to NT the amplitude of shortening was 34.7 ± 5.0% and 35.2 ± 6.8% with STZ and 41.0 ± 5.5% and 37.3 ± 5.7% with ALX stored for 15 and 60-120 min, respectively. During a 10 min NT washout STZ myocytes recovered to 56.2 ± 8.3% and 60.5 ± 8.2% and ALX myocytes recovered to 88.9 ± 10.0% and 83.7 ± 9.9% after storage of compounds for 15 and 60-120 min, respectively. Perfusion of the whole heart with ALX induced bradycardia but had no effects on the duration of action potential repolarization at 50% and 70% from peak action potential. The negative inotropic effects of STZ and ALX were not altered by storage. The results suggest that some of the effects on heart reported in STZ-and ALX-induced diabetes may be partly attributed to direct action of these compounds.
Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. ... more Cardiac microtubule stability is increased in the streptozotocin (STZ) model of type 1 diabetes. Here, we investigate the reason for increased microtubule stability, and the functional consequences of stable microtubule disruption. Ventricular myocytes were isolated from rats at 8-12 weeks after injection of STZ. A 10% increase in microtubule density, but no difference in the ratio of microtubule-associated protein 4 (MAP4) to tubulin was seen in myocytes from STZ rats. Functionally, STZ myocytes showed a tendency for reduced shortening and intracellular Ca2+ ([Ca2+]i) transient amplitude, and a significant prolongation of time to peak (ttp) shortening and [Ca2+]i. Although microtubules in STZ myocytes were less sensitive to the microtubule disruptor nocodazole (NOC; 33 microM) than control myocytes, we only saw marked functional consequences of microtubule disruption by NOC in myocytes from diabetic animals. NOC increased shortening and [Ca2+]i transient amplitude in STZ myocytes by 45 and 24%, respectively (compared with 4 and 6% in controls). Likewise, NOC decreased ttp shortening and [Ca2+]i only in STZ myocytes, such that these parameters were no longer different between the two groups. In conclusion, stable microtubules in diabetes are not associated with an increase in MAP4, but are functionally relevant to cardiac dysfunction in diabetes, regulating both [Ca2+]i and shortening.
Cardiac dysfunction is a frequently reported complication of clinical and experimental diabetes m... more Cardiac dysfunction is a frequently reported complication of clinical and experimental diabetes mellitus. Streptozotocin (STZ)-induced diabetes in rat is associated with a variety of cardiac defects including disturbances to heart rhythm and prolonged time-course of cardiac muscle contraction and/or relaxation. The effects of carbenoxolone (CBX), a selective gap junction inhibitor, on heart rhythm and contractility in STZ-induced diabetic rat have been investigated. Heart rate was significantly (P < 0.05) reduced in Langendorff perfused spontaneously beating diabetic rat heart (171+/-12 BPM) compared to age-matched controls (229+/- 9 BPM) and further reduced by 10(-5) M CBX in diabetic (20%) and in control (17%) hearts. Action potential durations (APDs), recorded on the epicardial surface of the left ventricle, were prolonged in paced (6 Hz) diabetic compared to control hearts. Perfusion of hearts with CBX caused further prolongation of APDs and to a greater extent in control compared to diabetic heart. Percentage prolongation at 70% from the peak of the action potential amplitude after CBX was 18% in diabetic compared to 48% in control heart. CBX had no significant effect on resting cell length or amplitude of ventricular myocyte shortening in diabetic or control rats. However, resting fura-2 ratio (indicator for intracellular Ca(2+) concentration) and amplitude of the Ca(2+) transient were significantly (P < 0.05) reduced by CBX in diabetic rats but not in controls. In conclusion the larger effects of CBX on APD in control ventricle and the normalizing effects of CBX on intracellular Ca(2+) in ventricular myocytes from diabetic rat suggest that there may be alterations in gap junction electrophysiology in STZ-induced diabetic rat heart.
Ventricular electrical conduction has been investigated in the streptozotocin (STZ)-induced diabe... more Ventricular electrical conduction has been investigated in the streptozotocin (STZ)-induced diabetic rat. Diabetes was induced with a single injection of STZ (60 mg/kg bodyweight, ip). The ECG was measured continuously, in vivo, using a biotelemetry system. Left ventricular action potentials were recorded with an extracellular suction electrode. Expression of mRNA transcripts for selected ion transport proteins was measured in left ventricle with real-time RT-PCR. At 10 weeks after STZ treatment, in vivo heart rate (HR) was reduced (267 +/- 3 vs. 329 +/- 5 BPM), QRS complex duration and QT interval were prolonged in diabetic rats compared to controls. In vitro spontaneous HR was reduced and paced heart action potential repolarization was prolonged in diabetic rats compared to controls. The mRNA expression for Kcnd2 (I (to) channel) and Kcne2 (I (kr) channel) was significantly reduced in diabetic rats compared to controls. Altered gene expression and, in particular, genes that encode K(+) channel proteins may underlie delayed propagation of electrical activity in the ventricular myocardium of STZ-induced diabetic rat.
Diabetes induces changes in the structural, biochemical, electrical, and contractile properties o... more Diabetes induces changes in the structural, biochemical, electrical, and contractile properties of skeletal muscles. Neuropeptide Y (NPY) administered locally can induce angiogenesis in a rat ischemic limb model and restore the contractile function of the ischemic muscle. The effects of NPY on the contractile characteristics of limb skeletal muscles were examined in streptozotocin-induced diabetic rats. Rats were treated with sham pellets (control groups) or NPY-containing pellets (1 mg of NPY/pellet, 14 days releasing time) administered locally to the rat hind limb 2 months after induction of diabetes. Contractile properties and fatigability of the slow-twitch soleus and fast-twitch gastrocnemius medials muscle were compared in control (sham), control NPY, diabetic (sham), and diabetic NPY groups. In order to induce fatigue trains of repetitive tetanic stimulation were used (600 ms/1 s simulation-rest cycle per train, 112 trains at an 85-Hz fusion frequency). Two months of untreated diabetes significantly prolonged soleus contraction and slowed its relaxation, but had minimal effects on soleus tension. NPY ameliorated the diabetic effects on soleus speed-related contractile properties, restoring its contraction and relaxation times. Diabetes significantly reduced gastrocnemius medials tetanic tension, leaving its contractile characteristics mostly unaffected. NPY partially restored gastrocnemius tetanic tension production capacity. Diabetes significantly increased fatigability of both muscles, which was partially restored by NPY, as evidenced by restored endurance of soleus muscle. The results suggest that NPY administered locally tends to normalize muscle performance and improve fatigue resistance of skeletal muscles in streptozotocin diabetes. Further examination is needed to establish the mechanisms of local NPY action on muscle contractile properties in streptozotocin-induced diabetes.
Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a d... more Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca 2+ , measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88 ± 2 ms and 107 ± 4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca 2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.
Diabetes mellitus is a serious global health problem, and cardiovascular complications are the ma... more Diabetes mellitus is a serious global health problem, and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. The chronic effects of neonatal alloxan-(ALX) induced diabetes mellitus on ventricular myocyte contraction and intracellular Ca 2? transport have been investigated. Ventricular myocyte shortening was measured with a video edge detection system and intracellular Ca 2? was measured in fura-2 loaded cells by fluorescence photometry. Diabetes was induced in 5-day old male Wistar rats by a single intraperitoneal injection of ALX (200 mg/kg body weight). Experiments were performed 12 months after ALX treatment. Fasting blood glucose was elevated and blood glucose at 60, 120 and 180 min after a glucose challenge (2 g/kg body weight, intraperitoneal) was elevated in diabetic rats compared to age-matched controls. Amplitude of shortening was significantly (P \ 0.05) reduced in electrically stimulated myocytes from diabetic hearts (5.70 ± 0.24%) compared to controls (6.48 ± 0.28%). Amplitude of electrically evoked Ca 2? transients was also significantly (P \ 0.05) reduced in myocytes from diabetic hearts (0.11 ± 0.01 fura-2 ratio units) compared to controls (0.15 ± 0.01 fura-2 ratio units). Fractional sarcoplasmic reticulum Ca 2? release was not significantly (P [ 0.05) altered in myocytes from diabetic heart (0.70 ± 0.03 fura-2 ratio units) compared to controls (0.72 ± 0.03 fura-2 ratio units). Amplitude of caffeine-stimulated Ca 2? transients was significantly (P \ 0.05) reduced in myocytes from diabetic hearts (0.43 ± 0.02 fura-2 ratio units) compared to controls (0.51 ± 0.03 fura-2 ratio units). Area under the caffeine-evoked Ca 2? transient was significantly (P \ 0.05) reduced in myocytes from diabetic heart (0.77 ± 0.06 Vsec) compared to controls (1.14 ± 0.12 Vsec). Intracellular Ca 2? refilling rate during electrical stimulation following application of caffeine was significantly (P \ 0.05) slower in myocytes from diabetic heart (0.013 ± 0.001 V/sec) compared to controls (0.031 ± 0.007 V/sec). Depressed shortening may be partly attributed to depressed sarcoplasmic reticulum Ca 2? transport in myocytes from neonatal ALX-induced diabetic rat heart. Keywords Neonatal alloxan-induced diabetes mellitus Á Alloxan-induced diabetes mellitus Á Type 2 diabetes mellitus Á Cardiac muscle contraction Á Intracellular Ca 2? transport Á Ventricular myocyte shortening
In this article, the name of the last co-author is given as Ljubisavijevic M. Dr. Ljubisavljevic ... more In this article, the name of the last co-author is given as Ljubisavijevic M. Dr. Ljubisavljevic surname is misspelled. His correct name should read ''Ljubisavljevic M''. Everything else in this article remains correct.
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